The present invention relates to a piston-drive mechanism in which a revolving wobble plate is driven by a driving shaft. The angle of inclination of the wobble plate relative to the driving shaft is adjustable. The adjustable inclination is achieved through an articulated connection of the wobble plate to the shaft by means of an axially movable guiding device as well as a driver arm that engages the wobble plate at a radial distance from the shaft to transmit the driving force from the shaft to the wobble plate. The pistons move parallel to the driving shaft. Each of the pistons has a glider element that is coupled to the piston with ball joint-like mobility. As the revolving wobble plate is in gliding engagement with the glider element, the rotation of the wobble plate results in a reciprocating axial movement of the piston. The wobble plate, which has the shape of an annular disk, has a cavity at one location of the circumference, with an opening of the cavity facing towards the center of the disk. The aforementioned driver arm, which is rigidly connected to the driving shaft, has at its free end a head that extends into the cavity, so that the driving force is transmitted to the ring-shaped wobble plate through the engagement of the driver arm head with the cavity wall inside the wobble plate.
A wobble plate piston mechanism of this kind is disclosed in DE 197 49 7272 A1, where the driver arm has a ball-shaped driver arm head extending into a cylindrical cavity of the wobble plate, also referred to as engagement cavity. The driver arm of this mechanism may also be referred to as torque transmitter, and the wobble plate is alternately referred to as annular swivel disk or swivel ring. The contact between the driver arm and the annular wobble plate takes place along the contact circle between the spherical driver arm head and the cylindrical engagement cavity, whereby the contact area is maximized. In this mechanism, the arrangement of a spherical driver arm head and a cylindrical engagement cavity has the disadvantage, that the gliding surfaces of the annular wobble plate are deformed into an uneven shape, which interferes with a smooth gliding of the glider elements (also referred to as glider shoes) on the annular wobble plate. In the vicinity of the cylindrical bore cavity of the wobble plate, where the spherical driver arm head applies an axial force parallel to the driving shaft, there is only a thin wall of material left between the cavity and the gliding surface so that this surface portion is subject to a strong deformation. Because of the uneven gliding surface, the glide shoes will not glide smoothly on the annular wobble plate.